A non-aqueous electrolyte secondary battery is well known which uses an alkali metal ion as an electrolyte ion (a guest cation), especially, a lithium-ion cell using a lithium ion is well known. In a next-generation lithium ion cell used for an electric vehicle battery, olivine phosphate compound represented as LiMPO4 attracts attention as a next-generation cathode active material instead of a transition metal oxide expressed as conventionally-used LiMO2 (M represents a transition element) On the other hand, a carbonaceous material such as graphite is mainly used for an anode.
However, since a phosphate polyanion has a relatively-high molecular weight in the olivine phosphate cathode, a theoretical capacity of the cell (theoretical energy density and a reversible capacity) is limited. For example, the theoretical capacity of LiFePO4 does not exceed 170 mAh/g. When a material which includes anions with a higher electronegativity is used as material of the cathode, the higher energy density can be obtained in theory. The inventors previously proposed the use of a metal fluoride as a cathode active material for a non-aqueous electrolyte secondary battery (Japanese Patent Application Publications JP-A-Heisei 9-22698A and JP-A-Heisei 9-55201). These metal fluorides have a theoretical energy density (the reversible capacity) higher than that of the olivine cathode material such as LiFeFO4, and, for example, a FeF3/Li cell is assumed to have a theoretical energy density as much as approximately 240 mAh/g, according to J. Power Sources, (68, p. 716 1997) by H. Arai, et al.